Fossil fuels are known to have the disadvantages of being a finite resource and a cause of global warming. As such, there has been much research on alternative fuels due to these ecological and economical considerations. Among the alternative fuels, dimethyl ether (DME) is a clean fuel, and can be synthesized from synthesis gas, also known as syngas. Synthesis gas is a mixture of mainly hydrogen, carbon monoxide and carbon dioxide that can be generated from a variety of different primary sources. These primary sources can include natural gas, coal, heavy oil, and also from biomass. The syngas is passed over a catalyst to produce methanol according to the following chemical equation:CO+2 H2→CH3OH
Methanol can then be converted into DME by dehydration over an acidic catalyst according to the following chemical equation:2 CH3OH→CH3OCH3+H2O
In the direct DME production there are mainly two overall reactions that occur from synthesis gas. These reactions, reaction (1) and reaction (2), are listed below.3 CO+3 H2 CH3OCH3+CO2  (1)2 CO+4 H2 CH3OCH3+H2O  (2)
Reaction (1) is a combination of three reactions, which are methanol synthesis reaction, methanol dehydration reaction, and water gas shift reaction:2 CO+4H2→2 CH3OH  (methanol synthesis reaction)2CH3OH→CH3OCH3+H2O  (methanol dehydration reaction)CO+H2O→CO2+H2   (water gas shift reaction)
The reaction (1) has a stoichiometric ratio H2/CO of 1:1 and has some advantages over reaction (2). For example reaction (1) generally allows higher single pass conversions and less energy-consuming in comparison to the removal of water from the system in reaction (2).
Recently, attention has been directed towards the direct synthesis of dimethyl ether from synthesis gas using a catalytic system that combines a methanol synthesis catalyst and a catalyst for dehydration of said alcohol. Depending on the synthesis gas used, the catalyst might additionally show water gas shift activity. However, the processes for the preparation of dimethyl ether according to the prior art have the drawbacks that additional steps have to be taken to get an efficient DME production. Additionally, the catalyst used in the methods known in the prior art do not achieve the thermodynamic possibilities. Therefore it is still desirable to increase the yield of DME in the synthesis gas conversion, and do so in one step.